Accessory protein for SNARE | Specific function of Accessary protein | Ref. |
Complexins/synaphins | It is expressed in the brain. It is important for ultrafast exocytosis and facilitates spontaneous exocytosis of NTs. In addition, It can inhibits liposome or cell-cell fusion by clamping full zippering of the trans-SNARE complex. | [28] [97] - [99] |
Munc13 | It is necessary for ultrafast exocytosis of NTs. Munc13 removes the Munc18 capping from syntaxin, allow only one SNAP-25 molecule to bind syntaxin, whereby it prevents misfolding to the 2:1 complex. | [28] [100] - [102] |
Snapin | It is identified as a SNAP25-binding protein and is expressed in both neuronal and non-neuronal cells. Snapin stabilizes the coupling between synaptotagmin1 and the SNARE complex during Ca2+ -triggered ultrafast exocytosis at central nerve terminals. | [103] [104] |
Tomosyn | It is identified as a syntaxin-binding protein in rat brain cytosol. Tomosyn is a negative regulator of exocytosis because it’s over expression causes a significant reduction in exocytosis and its deletion causes enhanced neurotransmitter release through increased synaptic vesicle priming. | [105] [106] |
CAPS | CAPS was originally isolated from brain cytosol as a factor required for Ca2+-triggered LDCV exocytosis. CAPS binds independently to each of the three SNARE proteins and markedly accelerates SNARE-dependent liposome fusion in vitro by promoting transSNARE complex assembly. | [107] |
RIM | It is a binding partner for Rab3, a highly abundant protein in synaptic vesicles. RIM facilitate SNARE assembly by reversing autoinhibitory homodimerization of Munc13. | [108] |
CAST | CAST directly or indirectly binds CAZ proteins to form a large molecular complex at the active zone. CAST also binds to RIM1 and, indirectly, to Munc13-1 to form a ternary complex. Deletion of CAST selectively affects the exocytosis of inhibitory synapses by reducing the size of the RRP. | [10] |